The use of acupuncture has increased markedly in the US over the last three decades. Although NCCAM is sponsoring clinical trials on acupuncture in cardiovascular disease, including hypertension, coronary artery disease or arrhythmias, the mechanisms underlying its influence are poorly understood. We have shown that electro acupuncture (EA) at the Neiguan acupoint over the median nerve reduces sympathoexcitatorycardiovascular reflex responses. Through an opioid mechanism, involving mu and delta receptors in the rostral ventrolateral medulla (rVLM), EA inhibits premotor sympathoexcitatory neurons that receive convergent input from the median and splanchnic (gallbladder) nerves. However, a long loop reflex likely exists involving the arcuate nucleus (ARC) and the caudal ventrolateral periaqueductal gray (PAG), in addition to the rVLM in the EA response. Preliminary anatomical and electrophysiological data suggest that these regions play a role in EA-cardiovascular response. The present proposal will use a combined neuroanatomical, electrophysiological and pharmacological approach to evaluate the role of the ARC and PAG in this response through three hypotheses. First, stimulation of the Neiguan acupoint increases c-Fos immunoreactivity in the ARC, PAG and rVLM whereas stimulation of the gallbladder increases c-Fos expression only in the PAG and rVLM. Cells in these regions will either be co-labeled or in close proximity to neurons or axons containing immunoreactive beta-endorphin or met-enkephalin. Second, EA increases activity in neurons of the ARC, which project to the PAG and through an opioid mechanism facilitates visceral somatic convergent inhibition in the PAG. Third, neurons in the PAG receiving convergent inhibition from the median and splanchnic nerves project to the rVLM where they inhibit evoked activity in sympathetic premotor neurons and the resulting cardiovascular responses. Understanding the pathways and the central neural integration by which EA at the Neiguan acupoint inhibits reflex excitatory cardiovascular responses will provide a greater understanding of the mechanisms underlying the beneficial modulation of the cardiovascular system by this alternative therapy. Such knowledge, along with the current clinical trials, will encourage acceptance of this therapy by scientists and clinicians in the US and other Western countries.